(a) Field of the Invention
The present invention relates to a plan achromat microscope objective lens system of medium magnification.
(b) Description of the Prior Art
There have generally been known objective lens systems which comprise thick meniscus lens components on the front and rear sides for flattening image plane and minimizing Petzval's sum of the lens systems as a whole. Such objective lens systems have long working distances (WD). However, the front lens group comprising a thick meniscus lens component on the object side unavoidably has a total focal length which is longer than that of a front lens group in an ordinary microscope objective lens system comprising no thick meniscus lens component. In the former type objective lens system, residual amount of longitudinal chromatic aberration in the front lens group increases almost proportionally to the focal length of the front lens group.
Further, the thick meniscus lens components arranged on the front and rear sides of the lens system have a common nature to remarkably aggravate longitudinal chromatic aberration and lateral chromatic aberration both in themselves and the entire lens system. In a lens system having such a composition, the thick meniscus lens components arranged on the front and rear sides result in undercorrection of astigmatism and overcorrection of distortion in addition to increase in chromatic aberration mentioned above.